With the parking brake system of the average motor vehicle, the initial movement of the parking brake pedal merely takes up the normal slack in the brake cable and in related mechanisms. There is a certain amount of lost motion that occurs in merely moving the brake shoes from their retracted position into contact with the brake drums. Relatively low efforts are required by the vehicle operator to move the parking brake pedal through this initial phase prior to the actual brake application.
It is an object of this invention, therefore, to provide a parking brake control for applying the parking brakes of a motor vehicle wherein the control effects a rapid movement of the brake shoe assemblies into engagement with the brake drums upon a relatively short initial stroke of the brake pedal and has an effective mechanical advantage ratio that is lower than is desired for high pressure brake application.
It is also an object of the invention to provide a brake control that accomplishes the foregoing object and wherein the effective mechanical advantage ratio is increased in response to both pedal displacement and brake cable tension when the brake shoes engage the brake drums thereby providing a greater force to apply the brake shoes with a lower effort requirement on the part of the vehicle operator.